But the images were particularly haunting for people who were at the World Trade Center on Sept. 11, 2001, and those who lost loved ones in that terrorist attack.

Sept. 11 first responders and family members said the Boston bombing brought back the terror of that day. They also predict that it will take a long time for the rescuers who ran to help the injured - as well as the victims and their families - to return to the life they knew before the bombs went off.

"You can never forget it," said John Leonard of Nanuet, N.Y., a retired lieutenant in the New York City Fire Department who took part in rescue and recovery efforts at the World Trade Center site. "It's etched in your mind forever."

Boston rescuers probably will have a similar reaction, he predicted.

"I can tell you what they felt and saw that day was similar to the day it happened to us," Leonard said.

The sight of a bomb exploding and shattering a city's sense of safety and normalcy probably will bring back vivid memories of Sept. 11 for many people, said Barbara Bernstein, a psychologist at the Mental Health Association of Westchester County, N.Y.

"Trauma has an ongoing impact on people," she said. "When similar events occur in the future, they are likely to trigger the emotions and maybe even the actual experience."

Sept. 11 rescuers and survivors can expect to experience many of the same feelings.

"They may have flashbacks and they may feel like they are almost back where they were on Sept. 11," Bernstein said.

Retired White Plains, N.Y., Fire Department Lt. John Donahoe was among the Westchester County, N.Y., firefighters who answered the call for help in the days right after the Sept. 11 attack.

He has never forgotten what he experienced.

And he imagines that police, firefighters and others who tended to the dying and wounded in Boston will have a similar reaction to what they experienced.

Maybe even more so, Donahoe said, because the bombing was so sudden and no one who attended the marathon expected to be in the middle of such carnage.

"It was such a glorious event on a glorious day and then to have that devastation, mutilation of people right in front of you - it's unfathomable," he said.

The memories of what Donahoe saw and experienced in the days after Sept. 11 will never go away. But he hopes the Boston first responders will realize something that struck him about the work he did in the emergency.

"There are horrific memories, but there are good ones, too," Donahoe said. "The good memories of working alongside so many dedicated people and bringing comfort to families when we were able to recover a body - those are part of the experience, too."

Some who lost loved ones on Sept. 11 found that devoting themselves to charitable work helped ease the pain - a strategy that Boston survivors might find helpful.

Mahopac, N.Y., resident Jay Winuk, whose brother Glenn was killed in the attacks, founded a group, My Good Deed, which encourages people to honor victims by pledging to perform an act of service every Sept. 11.

Winuk said he would never tell anyone how to grieve or recover from a loss, but his experience shows that it is possible to find some good even in a terrible situation.

"When the chips are down, Americans and good people all over the world rise to the occasion," he said. "Who knows what will come out of Boston?"